The importance of diagnostic systems for computer-controlled machinery, such as motor vehicles, is constantly growing together with the complexity of the systems. Vehicle onboard diagnostic systems (OBD) were developed to help diagnose and service the computerized engine systems of today's vehicles. Despite the type of vehicles OBD systems are installed in, they all function to diagnose component malfunctions that occur in the critical or essential systems required for the vehicle's proper operation and maintaining compliance with government regulations such as the engine and emissions controller systems, respectively.
These systems commonly operate to detect a malfunction or component deterioration before the driver becomes aware of a problem. However, nearly all systems include a means of notifying the driver that a problem exists in one of the components whenever a deterioration condition reaches a critical level. This indication is usually provided in the form of a malfunction indicating light found in the instrument cluster of a vehicle. Once noticed, the vehicle user is alerted that the vehicle is in need of some form of repair and thus should be taken in for service.
Although conventional OBD systems are operative to diagnose malfunctions in a general sense, these systems do not have the capability to determine a root cause or isolate the fault. The repairperson is typically provided one or more fault codes by the OBD system that describes the malfunction but not its cause. Thus, the repairperson is left with the responsibility of fault isolation. In some cases this results in the vehicle owner being deprived of access to his vehicle for several days until proper repairs can be made. Accordingly, there exists a need for a diagnostic system of computer-controlled machinery that not only can detect and describe a malfunction but also perform reliable and accurate fault isolation.